The invention mainly relates to sealed rotor motors for applications in which it is required to avoid contact between the stator of the motor and a dangerous liquid or gaseous environment.
A typical example of the application of such a motor is the control of a valve that shuts off the flow of gas to a boiler. The electrical parts of the motor (in practice the stator) must not be in contact with the gas. There are of course many other applications of such motors.
These motors are often constructed in the following manner: a rotor assembly equipped with a ball bearing is mounted in a massive support block that forms a partition separating the rotor environment from the stator environment. The ball bearing is mounted in a housing in this support block with the rotor projecting outside the housing. A stator assembly is mounted around the rotor and is fastened to the support block by screws, for example.
The present invention notably concerns the fitting of the ball bearing in the support block.
Since the invention is advantageously (though not exclusively) applicable to sealed rotor motors, before indicating the object of the invention, we shall also explain how the invention provides for sealing of the motor.
In a sealed rotor motor, it is necessary to separate the environment on the rotor side from the environment on the stator side and prevent for example any flow of gas via the ball bearing or via the air gap between the rotor and stator. To do this, a sealing bell is used to enclose the whole rotor assembly. The lateral, cylindrical, nonmagnetic wall of this bell is inserted into the rotor/stator air gap. The whole stator assembly, notably including the conductors feeding the stator, is located outside the bell. The bell also makes sealed contact with the support block, in other words with the solid wall separating the stator environment from the rotor environment, thereby ensuring that the two environments are separated from each other in a gas-tight manner. The bell encloses not only the rotor but also the ball bearing.
The invention proposes a particular way of mounting the ball bearing in the support block that is notably suitable for sealed rotor motors.
The ball bearing fits in the housing provided in this support block; the housing diameter is adjusted so that the bearing can be hand-fitted in the housing tightly but without friction. In prior art solutions the ball bearing was force-fitted; in some solutions in which it was hand-fitted a metal tongue or other means was necessary to immobilize-rotationally and axiallyxe2x80x94the fixed bearing race in the housing.
In the present invention, the fixed bearing race is immobilized by means of an elastic annular seal, preferably of O-ring type, inserted between the stator assembly of the motor and the periphery of the fixed race and compressed by the fastening of the stator assembly on the support block.
Once the ball bearing has been hand-fitted into the support block, with the rotor projecting outside this housing, the stator assembly is mounted around the rotor then fixed onto the support block, in general by screws, which also squeezes the annular seal against the fixed race of the bearing. This pressure also holds the bearing firmly in its housing, and the friction of the seal prevents the fixed race from rotating under the influence of the rotation of the rotor.
The invention is therefore an electric motor including a support block containing a ball bearing housing, a rotor that projects from this housing, and a stator assembly mounted around said rotor and fastened on said support block, characterized in that an annular seal, preferably of O-ring type, is squeezed between said stator assembly and the periphery of the fixed race of said ball bearing, the pressure of said annular seal preventing axial and rotational movement of said fixed race.
In the case of a sealed motor including a bell that encloses the rotor, the open end of the bell is bent radially outwards to form a rim (whose plane is therefore parallel to the plane of the annular seal) which is inserted between the stator assembly and the annular seal. This rim of the bell is held pressed against the seal by the tightening of the stator assembly on the support block. The seal bears not only on the periphery of the fixed bearing race (but without making a seal at this point), but also on part of the support block, which ensures sealing between the bell and the support block around the periphery of the bell.
The ball bearing housing preferably has, on the side on which the bearing is inserted, a peripheral section of diameter slightly greater than that at the bottom of the housing which holds the fixed bearing race, said seal being fitted in this wider section, the diameter and radial thickness of the seal being chosen such that the periphery of the seal presses against the internal cylindrical wall of this wider section.
With the arrangement of parts according to the invention, the bearing is not subjected to any excessive forces, which avoids any risk of deformation and enables optimal operation.
The degree of compression of the seal enables dimensional variations of the various parts to be taken into account in the presence of large temperature gradients, in order to ensure that the bearing remains firmly immobilized despite these temperature variations.
In the case of a sealed rotor motor the invention also provides for sealing.
Finally, the invention also includes an assembly process for the electric motor, including the following steps: preparation of a rotor assembly including a rotor and a ball bearing; fitting of this assembly in a ball bearing housing in a support block, with said rotor projecting outside the housing; fitting of an annular seal, preferably of O-ring type, against the fixed race of said ball bearing; fitting of a stator assembly around the rotor; and tightening of said stator assembly against said support block, this tightening squeezing said annular seal against said fixed race. For a sealed rotor motor, said stage of fitting of the stator assembly is preceded by a stage of fitting of a non magnetic sealing bell around said rotor, said bell having a rim bent radially outwards that presses against said annular seal and said stator assembly pressing against this rim to press it against said annular seal.